1. Field of the Invention
The present invention relates to optical fiber connector assemblies for connecting optical fiber cables and, particularly, to an optical fiber connector assembly to which an optical fiber cable is fixed later to complete an optical fiber connector assembly.
2. Description of the Related Art
Most of the conventional optical fiber connector assemblies require a bonding agent to assemble them in the field and have disadvantages in terms of environment and the number of manufacturing steps. The assemblers demand simpler and fewer manufacturing steps. There are some optical fiber connectors preassembled by optical fiber connector manufactures.
For example, Japanese patent application Kokai No. 7-248433 discloses a push-pull or SC type optical fiber connector. Two such connectors are connected through an adaptor type connector. It is easy to fix an optical fiber to the connector to complete the assembly without any bonding agent.
In the above connector, an optical fiber is fixed at two points by an elastic insert and a collapsible plunger. The elastic insert consists of three elastic balls of the substantially same diameter and placed behind the ferrule. The elastic balls are fitted into a narrow space to fix the fiber element. The collapsible plunger is made as an elongated cylinder and placed behind the elastic insert. The collapsible plunger is then fitted into a narrow cylindrical space so that projections of the collapsible plunger collapse to fix the optical cable.
In the above connector, however, the elastic insert for fixing the fiber element is prone to thermal deformation so that the optical cable is moved in the axial direction. That is, when the ambient temperature changes, the gripping power over the optical cable is lowered because of a difference in thermal expansion between the elastic insert and the optical cable so that the optical cable tends to move in the axial direction. Consequently, the position of the optical cable at the front end of the ferrule is shifted, resulting in the poor optical connection characteristics. (This is called "insertion loss change.") This insertion loss change is a factor to cause a connection loss of the optical cable. In the above example, the optical cable is fixed at points so that the fixation is unstable. That is, the elastic insert is spherical so that when it is shrunk, the fiber element contacts the balls at small areas. In addition, the projections behind the collapsible plunger occupy only a mere portion so that when the projections are collapsed, the areas that the optical cable abuts on the collapsed projections are small. Consequently, the fixing strength of the optical cable is low. Moreover, there is a large distance between the elastic insert and the collapsible plunger so that the thermal change of the jacket for the optical cable between them is very high, resulting in the weak optical cable and reducing the usable temperature range.